PROJECT SUMMARY Low voluntary calcium intakes have been implicated in several diseases that afflict the U.S. population including osteoporosis, hypertension, obesity, and premenstrual syndrome. But despite many recommendations to increase calcium intake there has been almost no research to understand why calcium intakes are so low. This project will address this question by identifying and characterizing some of the physiological and genetic controls that underlie calcium consumption. Two aims are proposed in this renewal application. The first is to identify genes responsible for the consumption of calcium. In Aim 1.1, congenic and consomic mice will be bred in order to isolate small chromosomal fragments containing consumption-related genes. In Aim 1.2, candidate genes in each fragment will be assessed using a combination of in silico methods and gene expression studies. The second aim is to characterize the modes and sites of action of two genes that this project has already implicated in the control of calcium consumption; the calcium-sensing receptor, Casr, and the sweet taste receptor, Tas1r3. This will be done by comparing the receptor activity of a mouse strain that avoids calcium (the C57BL/6J or B6 strain) with a strain that drinks calcium avidly (the PWK/PhJ or PWK strain). The plan is to use an HEK cell expression system to compare the physiological responses of B6 and PWK forms of CaSR and T1R3 (Aim 2.1), in situ hybridization, real-time PCR, and immunochemistry to characterize the expression of the B6 and PWK forms of CaSR and T1R3 in taste tissue (Aim 2.2), and gustatory electrophysiology to determine the functional significance of any differences between the two strains in physiological response or location of CaSR and T1R3 (Aim 2.3). Aim 1 will lead to the discovery of genes involved in regulating the ingestion and metabolism of calcium. Aim 2 will test the possibility that a specific receptor or pair of receptors transduce calcium taste. Understanding the mechanisms underlying calcium perception is an important step toward answering the question of why calcium intakes are so low. Given the many similarities between the mouse and human genome, such studies in mice will have direct relevance for the control of calcium consumption by humans, and thus the many diseases associated with excess or insufficient calcium intake.